In a copying device, it is required to execute a data processing such as a scanning or printing at a certain rate in accordance with a processing speed of an external device such as a DF and a print engine. Conventionally, there is known a technology which controls priority of data and keeps a transmission band of a common bus line in a predetermined band based on a data amount of a data part of transmission data transmitted via the common bus line.
However, in the conventional technology, there is a case in which it is difficult to keep the transmission band of the common bus line in the predetermined band without considering the data amount of a head part of the transmission data.